This invention relates to subsea wells and in particular to a method and apparatus for pulling in flow lines to the wellhead.
Offshore wells may be drilled hundreds and thousands of feet below the surface. When the well is to be produced a flow line must be pulled in and prepared for connection to a later installed production tree. These flow lines are pulled in and secured at a precisely predetermined location, so that when the production tree is installed it may be connected to both the wellhead and the flow line termination, whereby flow may be controlled and directed from the well to the flow line.
Typical systems for pulling in and connecting the flow lines are shown in U.S. Pat. Nos. 4,161,367, 3,866,677 and 4,382,717. In these the cable is passed through a pulley arrangement and attached to a bullnose at the end of the pipe to be pulled in. One end of the cable remains at the surface with the pull in tool being passed down to the wellhead. Tension is then applied at the surface to pull the flow line into the wellhead location.
Particularly, when dealing with deep wellheads, in the order of 7500 feet, this requires a long length of cable in the order of 9 to 10 thousand feet. This long cable has a potential for tangling. It also has considerable weight which must be handled and a considerable length of high strength cable, which must be stored on the floating vessel. The pull in system also has a poor response time because of the elasticity of the long length of pull in cable. Furthermore, emergency disconnect requires cutting of the cable and significant problems in reestablishing the pull in.